The servicing of vehicles is not limited to the routine lubrication needs, but includes periodic examination and adjustment in the alignment of the wheels. Normally the alignment of wheels may be examined most easily when the vehicle is raised to a convenient elevation. The raising is accomplished by placing the vehicle on a runway structure which then bodily raises the same. However, the wheels must support the vehicle at this time, and subsequently the wheels need to be elevated above the runway. A number of devices have been provided for accomplishing the latter function.
For example, an early device is disclosed in the Bristol U.S. Pat. No. 2,240,756 issued May 6, 1941. Here a jack carried by a runway hoist assembly is applied to the vehicle frame for vibrating the frame during the lubricating of the wheel and frame joints. It is also known from the MacMillan U.S. Pat. No. 3,563,345 issued Feb. 16, 1971, and from Masaitis U.S. Pat. No. 3,789,958, issued Feb. 5, 1974, that a twin-air cylinder lifting device carried by the elevated wheel runways could be used to raise the wheel for alignment servicing purposes. An improved twin-cylinder jack assembly is disclosed in Hunter U.S. Pat. No. 4,050,545 issued Sept. 27, 1977 in which safety ratchet and pawl means are used to prevent accidental dropping of the vehicle during wheel alignment servicing. A common characteristic of the foregoing patented devices was the arrangement whereby the devices could be folded into positions presenting a minimum dimension upon lowering the runways to the floor when receiving and discharging a vehicle.
The problem with the devices referred to above is that the folding characteristics requires certain extra structure and that increases the cost of production and subsequent maintenance during the useful life of the assembly. Furthermore, a foldable device must be prevented from returning to its folded position after being moved into the operative position and operated to raise a vehicle.